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Reduced Power Mode, No Codes or engine light

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35K views 14 replies 5 participants last post by  dmtcm  
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#1 ·
My stock 2008 LMM is going into reduced power mode. I've noticed it does this when hot and won't go off. Maybe when hot the fuel line gets soft and bends/pinches off? I drove it in the cool morning the other day and it was fine. All coolant and fluid levels are fine. I've done a search on here and understand it can be air flow or fuel lines. I just changed the air filter and it still does it. I've had them check codes with good scanners and nothing.

I'm going to check my fuel lines next. Thoughts?
 
#2 · (Edited)
I'd agree that fuel lines would be the next obvious culprit. Fuel filter life status change on DIC?
 
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#3 ·
Fuel filter was changed not long ago and looks good. I just checked the fuel lines starting in the back and they were all fine until I got to the two on the back right side of the engine where they make a 90 degree turn. Both the large and small ones were kinked. Now to figure out how to change those sections...
 
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#5 ·
So some info for all. If you call around for the recommended SAE 100R3 1/2" ID hose, everyone will tell you it's overkill and you can't clamp it. I can't say whether it's overkill but would guess it was contemplated in the service bulletin. Lots of the hose that meets this spec is woven on the outside. The recommended Parker 601-8 is not. The best supplier I found was at Hydradyne and it's about $6/foot.

Does anyone know the size of the smaller return hose? If it's kinked, I would imagine it's a problem and needs to be replaced as well...?
 
#6 ·
Have you checked your filter housing? They are prone to failure also.
 
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#7 ·
I haven't but figured it worked for 2k miles, why would that stop working all the sudden. I'll change it out just in case because it's a cheap fix and will eliminate that as a possible cause. No doubt the fuel lines are somewhat kinked. Many get codes thrown though and I am not...
 
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#8 ·
This one is starting to perplex me. I checked the fuel lines while the truck is running and none are kinked anymore and are solid when I squeeze them. Plus, it does it at idle and those that complained of the fuel lines usually had the symptom when under heavy load and/or pressure. To summarize:

1. I changed the air filter, but the old one was really dirty
2. I changed the fuel filter.
3. I'll change the fuel lines but they look ok when the truck is running.
4. I can't get it out of "reduced engine power" no matter if it's hot or cold out now.
5. No engine codes have ever been thrown.
6. It started under no load driving on the freeway about 55. I got the truck home. The next morning it worked normal for the 10 minutes I drove it. It's been in limp mode ever since.
7. Stock 2008 LMM truck, no mods. 150k

So I had ordered EFI Live and it will be here in a few days, coincidentally to this problem. Along with it, I was planning on deleting the DPF and I have an MBRP turbo back exhaust layed out to install. Should I:
A. Replace the exhaust, install the EFI Live and hope this does something to fix the truck? I have read some of the exhaust sensors or a clogged DPF can possibly cause this issue and this might fix it if it's DPF or exhaust sensor related. I would think this would throw a code though...?
B. Fix the issue before the exhaust and EFI Live update? My next ideas are to clean or get a new MAF and MAP sensor.

Thoughts?
 
#9 ·
Running a scan tool and watching the parameters while the engine is running would be the first thing I would do with no codes stored. This is a rare instance that no codes are displayed yet the engine goes into reduced power mode. The only time I saw this in one of my trucks, I found the ECM was the problem and was started by a faulty battery. Having no codes yet it wouldn't come out of limp mode was the clue. As the battery heated up, the plates inside it would warp causing the alternator to go to maximum output. This caused major voltage spikes to the entire system. I figured out the battery problem while watching the tech II setting in the drivers seat and noticed the dome lights suddenly got really bright but were pulsating from the alternator regulator. I went to voltage readings at the ecm and they went from 11 volts to 15 volts repeatedly. I replaced both batteries and the alternator hoping the problem would be solved but the reduced power mode was still there. Replaced the ecm and all was well. Find someone with a Tech II, MDI, J2534, ect. to be able to pull the codes from every computer on the truck. See if there are any codes in the other modules for loss of communication with the ecm. Check the grounds. Not knowing the area you live in but the truck is at the age for rust to start forming in the northern states where road salt is used alot. Have you driven in high water? Not that there hasn't been some rain in the mid west and north east lately. Sorry for the long post. My mind went into diagnosis mode!:crazy::help2:
 
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#11 · (Edited)
I'm pretty sure the EFI Autocal will do what you need but I would not load any tunes until you have the issue repaired. The V2 (I have a V2 not an Autocal) reads codes under the four parameters below and the ones in the MFG Set DTC's do not set off the SES dash light.

I had 2 codes in that section for lack of communication between the ECM and TCM that had not gone through enough drive cycles to illuminate the SES. The dash went buggy and went back to normal and something just-did-not feel-right when the truck shifted, that's when the 2 DTC codes were found...




EPA Current DTC's

EPA pending

MFG Set DTC's

MFG All DTC's
 
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#12 ·
Got my Autocal EFI Live this morning. Hooked it up, read the DTC, and it came up with ECM P2138. I guess the EFI Live reads codes where the cheap computer at Autozone doesn't.

Looks like this is an Accelerator Position Sensor issue. I unplugged the sensor, played with the wires, plugged it back in and the truck works perfect now. Crazy! A loose connection on a sensor can do so much havoc. Looks like for those that get this same issue here is one other quick thing to check before you replace filters, fuel lines, etc...

Thanks All!
 
#13 ·
The money I spent on my used V2 has been paid back when I retrieved the ECM, TCM codes and spent a few hours under the truck and found the large connection plug at the rear of the transmission not seated completely. Who knows if a shop would have found it and done work to the transmission and inadvertently fixed it in the process...
 
#14 ·
Make sure when you do the delete for emissions, I would clean your MAF with electrical cleaner. EFILive is awesome, setup my 08 for a tow tune with exhaust break.
 
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#15 ·
Glad you found the problem! :)
 
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